1. Field of the Invention
The present invention relates generally to assaying means and methods. More particularly, the invention relates to a self-contained and hand holdable assaying arrangement including a low level luminometer for detecting and quantifying low level luminescent emissions produced by a bioluminescent and or a chemiluminescent assaying reaction.
2. Description of the Prior Art
The production of light as a result of a chemical reaction is generally referred to as chemiluminescence. A chemiluminescent reaction usually produces product molecules in an electronically excited state. Such molecules return to a more stable state by the spontaneous emission of a photon, and hence, light is produced. If the reaction that produces light is biochemical, the phenomenon is referred to as bioluminescence.
A number of different species have developed the ability to emit light via bioluminescent reactions. These include, but are not limited to bacteria, fungi, fish, and insects. The luminescent materials from all organisms are termed luciferin, while the enzymes required for their conversion into a light signal are referred to as luciferase. Accordingly, these types of bioluminescent reactions are often termed `luciferase-luciferin reactions`. The most extensively studied bioluminescent organism is the common American firefly, photinus pyralis. Although, the complete mechanism for the light producing reaction in the firefly has not been fully elucidated, it is been long understood that along with luciferin and luciferase other substances including magnesium ion, ATP (adenosine triphosphate) and molecular oxygen are required for the luminescence.
A particularly useful and interesting application involving bioluminescent reactions and their emissions involves the measurement of adenosine triphosphate (ATP), a material central to metabolism in virtually all living cells. As ATP is necessary for all living organisms to function, it serves as an excellent marker to indicate the presence of living matter (e.g., bacterial and other microbial matter). Accordingly, if one can ascertain (with a reasonable accuracy) a quantity of ATP present in a sample or specimen, either through direct or indirect measurement, one can make a determination of the quantity of microbes, microbial matter, or more generally the amount of analyte present. As discussed above, the most common method employed to measure the levels of ATP present involves the use of a firefly luciferase-luciferin assaying reaction. A properly conducted luciferase-luciferin reaction will produce detectable and measurable levels of luminescent emissions--even with relatively small quantities of analyte available. However, it must be understood that the level of luminescent emissions generated by such assaying reactions may be quite low, say as low as a tenth of a pico-watt (or less). The measurement of levels of emission this low necessitates sensitive accurate detecting and measuring systems that include low noise and generally specialized components.
There are many systems known and available that employ photomultiplier tubes (PMTs) and cooled charge-coupled devices (CCDs) to measure low level of emissions produced by bioluminescent and chemiluminescent assaying reactions. However, when considering PMT based devices, their cost is relatively high and they are easily damaged by shock and vibration. Further, as these devices require a high voltage supply and temperature stabilization for proper operation, they are rarely employed in low cost, highly portable instruments. CCD based devices can also be expensive, especially when structured to provide the necessary sensitivity. They are generally considered to have dark noise levels that are too high. As a consequence, when CCD devices are employed, they are almost always operated at a cooled, controlled temperature (which is generally well below the ambient temperature).
Alternative and generally low cost photo-sensing devices may be found in a number of solid-state (semiconductor) photodetectors including avalanche photodiodes, silicon-carbide photodiodes, PIN photodiodes, etc. Avalanche photodiodes, which are typically operated in a photo-conductive mode, have excellent bandwidth characteristics and good sensitivity. However, they exhibit a `dark current` that is generally considered too high for very low level luminescent measurements, say at a `sub` pico-watt level or less. Avalanche-photodiodes are also more expensive than other semi-conductor photodiodes, and as with PMTs, are often cooled to reduce their dark current noise levels. Other solid-state photodiodes, for example Silicon-carbide photodiodes, are not appropriate for ATP assay measurements as they have a peak sensitivity in the ultraviolet spectrum, say in the range of 200 to 380 nano-meters. PIN photodiode detectors have generally not been considered to be sensitive enough to use in low level ATP assaying luminometers. This is indicated by the fact that photomultiplier tube (PMT) devices, as well as CCD based systems, have been used almost exclusively in luminometers to measure such low level emissions.
As skilled persons will appreciate, a variety of devices and systems are available in the art to accurately determine and or compare relative and specific levels of light and luminescent emissions. These systems may be fundamentally separated into two categories: active and passive. Active systems employ one or more generally high level optical sources, such as lamps and or lasers. These systems may include beam splitting components, mirrors, and multiple detectors. Skilled persons would realize that the level of luminescent emissions detected with these active systems may actually be quite high. Accordingly, a number of the these systems may not be considered by skilled persons to be associated with the measurement of `low-level emissions`.
In contrast, a passive system does not provide or include any lamps or other controlled light sources. These devices, which may be termed `luminometers`, are constructed with sensitive photo-detecting front ends that detect and measure the low level luminescent emissions of interest. These systems are generally bench or table top units, that are not highly portable and self-contained, and further, are relatively high cost units.
Assaying arrangements that employ bioluminescent assaying reactions to produce low levels of luminescent emissions require a means to collect a specimen or sample. Once a sample has been collected (say with a cotton tipped swab), the sample is assayed by exposure to suitable reagents and enzymes to cause the emissions-producing reaction to occur. The art provides many examples of luminometer apparatus that are employable in a lab or testing facility to measure emissions of an assaying reaction. However, these assaying arrangements are not provided in a self-contained and highly portable architecture. Therefore, such systems have not been usable, in the field. For example, if a cleanliness inspection is being conducted in a hospital or a restaurant's kitchen.
Skilled persons will therefore recognize the need for improved low level, self-contained and highly portable assaying apparatus. A most preferred apparatus would enable specimens to be collected, provide a suitable assaying enclosure, and quantify a volume of an analyte (of the specimen) by measuring relatively low level luminescent emissions produced by bioluminescent and or chemiluminescent assaying reactions associated with the assaying activities that are employed to investigate the specimen.
A full understanding of the present invention, including an understanding of a number of capabilities, characteristics, and associated novel features, will result from a careful review of the description and figures of several embodiments provided herein. Attention is called to the fact, however, that the drawings and descriptions are illustrative only. Variations and alternate embodiments are contemplated as being part of the invention, limited only by the scope of the appended claims.